A light-emitting diode is a type of semiconductor device that emits light when voltage is applied to it. Nitride light-emitting diodes commonly serve as semiconductor optical elements emitting blue or green light. When the lattice match of compounds is taken into consideration, nitride semiconductor crystals are generally grown on the sapphire substrate, and then the electrode structure is formed to create a nitride light-emitting diode. However, the sapphire substrate has high rigidity, low heat conductivity, and low electrical conductivity, and the electrostatic problem thereof is also a primary factor that restricts the heat dissipation of original LED chips. Moreover, in original LED chip structures, the electrode will shield a portion of light and thus the light-emitting efficiency will be decreased. Therefore, the flip chip LED structure was gradually developed.
Nowadays, inverting a prepared LED chip and then soldering it onto a package substrate is a common technique for producing flip chip LEDs. Since the chip is inverted, heat may be conducted from the semiconductor layer directly to the package substrate, thereby preventing problems caused by poor heat dissipation of the sapphire substrate. Additionally, in flip chip structures, the sapphire substrate is inverted so as to be located at the upward light-emitting surface. Since the sapphire substrate is transparent, the problem of light being shielded by electrodes may be solved.
Due to the advantages described above, flip chip LEDs have attracted increasing attention in the industry. There are more and more LED manufacturers devoting their efforts to the technical field of flip chip LEDs, with expectations of improving related techniques or reducing costs so as to speed up the development of flip chip LEDs in the semiconductor industry.